Australia's Science Forum

Can anyone help me . We tested a solution made from our glucose solid, and it showed positive for Benedict's reagent when heated
The only thing i can think of is the gelatin is contaminated with glucose somehow.
Has anyone else got any ideas - any other reason this may be occurring?

We have just done some research.Benedict's contains blue copper sulfate (CuSO4).5H2O which is reduced to red copper oxide. The copper oxide is insoluble in water and so forms a precipitate.. so when you put it in a glucose solution in a test tube and then put this into hot water bath, the result is the brick red.
Biuret test for protein is a combination of copper sulfate and sodium hydroxide. IF you put this into a test tube containing gelatin solutions and put it into a hot water bath, you get the same result as you do for Benedict's reagent - due to the copper sulfate being reduced to copper oxide.
In a class situation, students are usually told which test to put into the hot water bath and so you probably would not see the 'false' result from protein.
In an exam situation, students here were given unknown solutions to test - one being protein and one being glucose. They were given all the usual food test reagents to use on each 'unknown'. They put everything into the hot water baths and got crazy results.
Isn't science wonderful

I don't think you are supposed heat the test for protein. We don't use Biuret as such we use dropper bottles of CuSO4 and NaOH. The positive for this is a mauve /purple colour which gelatin reacts to and glucose doesn't.
For benedicts you heat and get an orange colour and gelatin shouldn't react with this only glucose.

No, you are not to heat the protein solution. We use very weak CuSO4 solution and 2M NaOH, It produces mauve colour.
Benedicts gives you red brick after heating glucose.
L

PS You only need traces of glucose to give you a positive results, our darlings often swap lids on dropper bottles and that would be enough to contaminate gelatin.

Yep, all the above
I'm sitting here with my new tablet on fathers day and remembering all those times when things went wrong in prac tests and LMAO instead of tearing my hair out
I feel for you sunray but I now have a life
Ha Ha!

Good to hear from you Ocker, so glad you have a life! Does it begin after school?
I know you aren't supposed to heat Biurets, but of course, in a prac exam, students do things like this. Note to all - in a prac test never ever combine both biuret test and Benedicts. In classes the students are always told which test to heat, in a prac exam they are not - so they heated everything, even the starch/iodine.

BTW,
for us more mature labbies what does LMAO stand for, Ocker? I am planning to get a life at the end of this year, so I need to know all this important short cuts

Betcha it stands for "laugh my a--- off". In politer terms - rear end. Am I right Ocker?

Right on sister.
I saw anemail once with all the abreviations especially those pertaining to seniors

OMG,
that's what I am "a senior"